Electron microscopic cytochemical studies will be performed on cells of the gastric glands in order to visualize certain cellular changes during the process of hydrochloric acid secretion. Special reference will be made to demonstrate "gap junctions," "unit particles" of activity, and adenosine triphosphatase activity in parietal cells. Additional studies will be conducted on autolysosome formation in parietal cells following administration of compounds found in contraceptive drugs. Experiments also will be conducted to study the proliferative activity of the gastric mucosa following small bowel resection. Specific studies will be conducted to determine changes in (a) surface area, (b) weight, (c) thickness, and (d) cell counts on the gastric mucosa following resection. Electron microscopic studies also will be performed to determine the source of the new gastric epithelial cells in the rat with a small bowel resection.